Don't drop new table if there are any @triggers_not_dropped.

t/pt-online-schema-change/samples/plugins/make_drop_trigger_fail.pm

@@ -0,0 +1,36 @@
+package pt_online_schema_change_plugin;
+
+use strict;
+use warnings FATAL => 'all';
+use English qw(-no_match_vars);
+use constant PTDEBUG => $ENV{PTDEBUG} || 0;
+
+sub new {
+   my ($class, %args) = @_;
+   my $self = { %args };
+   return bless $self, $class;
+}
+
+sub init {
+   my ($self, %args) = @_;
+   print "PLUGIN: init()\n";
+   $self->{orig_tbl} = $args{orig_tbl};
+}
+
+sub before_drop_triggers {
+   my ($self, %args) = @_;
+   print "PLUGIN: before_drop_triggers()\n";
+
+   my $dbh      = $self->{aux_cxn}->dbh;
+   my $orig_tbl = $self->{orig_tbl};
+
+   # Start a trx and get a metadata lock on the table being altered.
+   $dbh->do('SET autocommit=0');
+   $dbh->{AutoCommit} = 0;
+   $dbh->do("START TRANSACTION");
+   $dbh->do("SELECT * FROM " . $orig_tbl->{name});
+
+   return;
+}
+
+1;